Part I: This project will define the effects of plasma ionized calcium concentration ((Ca ions)) on canine left ventricular global and regional function in the presence of regional myocardial ischemia. We will correlate biochemical changes, including ((Ca ions)) in epicardial venous blood draining ischemic myyocardium with regional left ventricular function, regional myocardial blood flow and myocardial adenosine triphosphate content and assess the effects of systemic ((Ca ions)) on these variables. We will also define the modulation of the inotropic effects of dopamine and norepinephrine by ((Ca ions)). Part II: The aims of this part of the proposal are to continue the development of a sensitive laboratory model for comparing the efficacy of cardioplegic solutions in the preservation of myocardial function during intraoperative ischemic arrest and to use this model to test the efficacy of a new slow-channel calcium blocking drug, nifedipine, as a myocardial protective agent. Part III: The aim of this part of the proposal is to examine in a randomized, prospective manner the differences, if any, between hypothermic cardioplegics solutions containing potassium, potassium plus albumin or potassium plus mannitol in three groups of patients undergoing aortocoronary bypass grafting. Part IV: The aim of this project is to determine precise volumetric correlations of multi-gated technetium-99m blood pools scans with measured left ventricular volumes in dog hearts. Part V: We will evaluate the technique of seven pinhole tomographic myocardial imaging using Thallium-201 (201Tl) to determine if it is prctical and more accurate in measuring.